1. Field of the Invention
The present invention relates to an image-forming device such as a printer, more specifically to the management of a consumable component in such a device.
2. Description of the Related Art
One example of an image-forming device in which the present invention can be practiced is the tandem color electrophotographic printer 1 shown in FIGS. 17 and 18: FIG. 17 is a side sectional view; FIG. 18 is a schematic block diagram of the printing engine.
The printer in these drawings has a low-voltage power source 2, a high-voltage power source 3, and four printing mechanisms: a yellow (Y) printing mechanism 4, a magenta (M) printing mechanism 5, a cyan (C) printing mechanism 6, and a black (K) printing mechanism 7. The printing mechanisms include respective photosensitive drum units (ID units) 4a-7a, light-emitting diode (LED) heads 4b-7b, discharge lamps 4c-7c, and transfer rollers 4e-7e, and are driven by respective motors 4d-7d. 
Printing media such as sheets of paper, not shown, are placed in a cassette tray 8, and fed into the printer 1 by the rotation of a hopping roller 9. An attraction roller 10 generates a static electric charge that holds the printing media to a transfer belt in a transfer belt unit 11. Driven by the rotation of a transfer-belt driving roller 11a, the transfer belt carries the printing media past the printing mechanisms 4-7, which perform printing processes that transfer yellow, magenta, cyan, and black toner images onto the printing media. The media next pass through a fuser 12, which fuses the toner images onto them, and are finally delivered into a stacker 13. The printing media may also be supplied manually, in which case they are fed into the printer 1 by a front roller 14, but the subsequent printing operations are the same.
These printing operations are controlled by the engine controller 15 in FIG. 18. The engine controller 15 controls the LED heads 4b-7b through a relay board 16, and directly controls the discharge lamps 4c-7c, the above-mentioned motors (M) 4d-7d, a hopping motor 9d that drives the hopping roller 9, a belt motor 11d that drives the transfer-belt driving roller 11a, a heater motor 12d that drives a heating roller in the fuser 12, a front motor 14d that drives the front roller 14, and the power sources 2, 3. The low-voltage power source 2 supplies power to a heat source such as a halogen lamp (not shown) in the fuser 12. The high-voltage power source 3 supplies power to the ID units 4a-7a and the transfer belt unit 11. The engine controller 15 is also connected to various sensors 17, such as a sensor that senses the presence of printing media and a sensor that senses whether the printer""s cover is open or closed.
In this printer 1, the ID units 4a-7a, the transfer belt 11, and the fuser 12 are consumable components that must be replaced at the end of their service lives. To tell the user when to replace the consumable components, the printer has counters that count the cumulative number of rotations made by rotating parts such as the photosensitive drums. When a counter reaches a predetermined value, the printer displays a service-life alarm indicating that the corresponding consumable component needs replacement. Notified by this alarm, the user can replace the consumable component at the appropriate time.
When the consumable component is replaced, it is also necessary to reset the counter. It is known art to reset the counter automatically by means of the structure shown in FIG. 19. The consumable component 20, which may be any one of the ID units 4a-7a, or the transfer belt 11 or fuser 12, includes an internal fuse F1. The printer has a consumable-component sensing section 18 that senses whether the fuse F1 is blown. If the fuse F1 is not blown, the consumable-component sensing section 18 blows it and resets the counter.
The consumable-component sensing section 18 includes a transistor TR1, a resistor R1, and a central processing unit (CPU) 19, the functions of which will be described below with reference to the flowchart in FIG. 20.
When the printer""s power is switched on or its cover is opened and then closed, to determine whether the consumable component 20 has been replaced, the CPU 19 reads (step S201) and tests (step S202) the input value at a one-bit digital input port IN, which is connected through fuse F1 to ground and through resistor R1 to a power supply (Vcc). If the input value is at the high logic level, indicating that fuse F1 is already blown and the consumable component 20 is not new, the CPU 19 terminates the process in FIG. 20. If the input value is at the low logic level, indicating that fuse F1 is not blown and the consumable component 20 is new, the CPU 19 resets the counter that keeps track of the service life of the consumable component 20 (step S203), and outputs a xe2x80x980xe2x80x99 pulse from an output port OUT (step S204), sending a current pulse through transistor TR1 to blow fuse F1. To confirm that fuse F1 has blown, the CPU 19 reads (step S205) and tests (step S206) the input value at the input port IN again. If the input value is at the high logic level, the process ends; if the input value is at the low logic level, steps S204, S205, and S206 are repeated until the input value becomes high, or until a limit number of repetitions is reached.
Consumable components such as the ID units, transfer belt, and fuser have different specifications for different printers, and when they are replaced, the user may mistakenly install a consumable component of the wrong type. Since there are four ID units with different toner colors, the user may also install an ID unit of the wrong color.
When this happens, a conventional printer cannot recognize that the consumable component has been incorrectly replaced, and operates as if the replacement had been made correctly, creating various problems. One problem is that the user does not realize that the wrong consumable component has been installed until a defective printing result is obtained, at which point the user must replace the consumable component again, repeat the printing job, and either dispose of the consumable component that was mistakenly installed, or store it for later use. Another problem is that the mistakenly installed consumable component now has a blown fuse, so if it is later reinstalled and used, its counter will not be reset, and its service life will not be indicated correctly.
If consumable components with different specifications or colors have different external shapes, these problems can be avoided by a mechanical interlocking mechanism that prevents the installation of the wrong type of consumable component, but such mechanisms increase the manufacturing cost of the printer and the consumable component.
Instead of a fuse, the consumable component may have an internal memory circuit storing, for example, identification information and either a count value or a flag indicating whether the consumable component is new or not, but this memory circuit also increases the cost of the consumable component.
Another problem is that when a new consumable component is installed, its fuse may fail to blow. In this case, a conventional printer displays an alarm indicating that the consumable component is defective, and disables printing. The user must then replace the consumable component again, even though its functioning is not normally impaired by the fuse failure, and the failure may be due to a temporary condition that will disappear later.
A further problem is that the printer cannot distinguish between the state in which the consumable component is not installed, and the state in which the consumable component is installed but has a blown fuse. One conventional solution to this problem is shown in FIG. 21. The consumable component 20 and sensing section 18 make electrical contact at three points 21, 22, 23. In the consumable component 20, contact point 22 is coupled directly to contact point 21, and is coupled to contact point 23 through the fuse F1. The consumable-component sensing section 18 now includes a transistor TR1, resistors R11-R16, a CPU 19 with input ports IN1 and IN2, and switching means (not shown) for making and breaking electrical contact at points 21 and 23. In the consumable-component sensing section 18, contact point 22 is coupled to the power supply (Vcc) through resistor R11, and contact point 23 is grounded. The functions of these elements will be explained with reference to the flowchart in FIG. 22.
When the printer""s power is switched on or its cover is opened, then closed, the CPU 19 commands the switching means to make electrical contact at point 21 (step S211), then reads and tests the input value at input port IN1, which is connected through resistor R15 to contact point 21 and through resistor R16 to ground (step S212). If the IN1 input value is at the low logic level, indicating that the consumable component 20 is not installed, the CPU 19 displays an alarm indication on, for example, a display panel (step S213), then terminates the procedure.
If the IN1 input value is at the high logic level, indicating that the consumable component 20 is installed, the CPU 19 commands the switching means to break the electrical contact at point 21 and make electrical contact at point 23 (step S214), then reads and tests the input value at input port IN2, which is connected through resistor R13 to contact point 22 and through resistor R14 to ground (step S215). If the IN2 input is at the high logic level, indicating that fuse F1 is already blown, the CPU 19 terminates the procedure. If the IN2 input value is at the low logic level, indicating that fuse F1 is not blown, the CPU 19 resets the counter that keeps track of the service life of the consumable component 20 (step S216), and outputs a xe2x80x980xe2x80x99 pulse from output port OUT (step S217), sending current through transistor TR1 and resistor R12 to blow fuse F1, then reads and tests the IN2 input value again (step S218). Steps S217 and S218 are repeated until the IN2 input goes high, or until a limit number of repetitions is reached.
The conventional art shown in FIGS. 21 and 22, like that in FIGS. 19 and 20, has the drawback of being unable to distinguish between different types of consumable components. A further disadvantage is the need for a third electrical contact point 21, and the need for switching means for making and breaking the electrical contacts at points 21 and 23. The third contact point and switching means both take up extra space. The switching means also adds to the complexity of the printer and increases its cost.
The problems described above are not limited to electrophotographic printers, but can occur in other types of image-forming devices as well.
One object of the present invention is to provide an image-forming device with low-cost means for preventing the mistaken installation of an incorrect type of consumable component.
Another object of the invention is to enable a consumable component in an image-forming device to be used despite the temporary failure of a fuse to blow.
A further object is to enable a consumable component with a blown fuse to be distinguished from a consumable component that is not installed without the need for an extra electrical contact point.
A still further object of the invention is to provide a convenient means of monitoring the temperature inside the image-forming device.
The invented image-forming device has a replaceable consumable component with an internal fuse. When the consumable component is installed, the fuse is blown to indicate that the consumable component is no longer new. In addition, a counter in the image-forming device may be reset; thereafter, the counter measures the remaining service life of the consumable component by counting a predetermined repetitive operation that is executed when the consumable component is used.
According to a first aspect of the invention, the consumable component includes a resistor connected to, e.g., connected in series with the internal fuse. The resistance value of the resistor indicates the type of consumable component. Before blowing the fuse, the image-forming device determines the type of the consumable component. For instance, it determines whether the consumable component is of the correct type by measuring the resistance value of the resistor, and warns the user if the consumable component is of an incorrect type.
The image-forming device may also have means for short-circuiting the two ends of the fuse, so that the resistance value of the resistor can be measured even after the fuse has been blown. This feature is useful when the consumable component is temporarily removed, then reinstalled.
In an electrophotographic printer with replaceable photosensitive drum units having different toner colors, the resistance value may indicate the toner color.
The image-forming device may also have means for enabling the user to decide whether or not to reset the counter and blow the fuse when a consumable component of the correct type is installed. This enables the consumable component to be tested without blowing its fuse.
According to a second aspect of the invention, the image-forming device has a memory that stores fuse defect information. While attempting to blow the fuse in the consumable component, the image-forming device measures its resistance, first to decide whether the resistance is normal, then to determine whether the fuse has blown. If the fuse has normal resistance but fails to below within a predetermined time, the fuse defect information is checked. If this information does not indicate that the fuse had failed to blow in a previous attempt, then the counter is cleared and the consumable component is used for the time being, but its failure to blow is recorded in the memory, so that if the fuse again fails to blow on the next attempt, an alarm warning can be given. If the fuse is blown successfully on the next attempt, the indication of its failure to blow is cleared in the memory.
Before attempting to blow the fuse, the image-forming device may use a resistance measurement to determine whether the fuse is already blown, and if it is, clear the indication in the memory without resetting the counter.
If the replaceable consumable component is a photosensitive drum unit having a photosensitive drum making contact with a transfer roller through which current is supplied to charge the surface of the photosensitive drum, before measuring the resistance of the fuse, the image-forming device may measure the output voltage of the power source that supplies the current, to confirm that the photosensitive drum unit is properly installed, so that an uninstalled photosensitive drum unit will not be misinterpreted as an installed photosensitive drum unit with a blown fuse. If the photosensitive drum unit is not installed, the indication in the memory is not cleared and the counter is not reset.
According to a third aspect of the invention, the consumable component includes a resistor connected in parallel with the internal fuse between two points at which the consumable component makes electrical contact with the image-forming device. The electrical resistance between these two points then indicates whether or not the consumable component is installed, and if it is installed, whether or not its internal fuse is blown. The resistance value may also indicate whether the consumable component is of the correct type. The resistor may be a thermistor with a positive temperature coefficient, in which case the resistance value can be monitored to monitor the temperature inside the image-forming device.
The invention also provides a consumable component such as a photosensitive drum unit or a toner cartridge having a resistor coupled in parallel with an internal fuse.